The class of drugs exhibiting opium or morphine-like properties is referred to as opioid agonists, or opioids, and they interact with opioid receptors in the brain, the peripheral nervous system and other tissues. The three major opioid receptor subtypes are mu, delta, and kappa. Each of these receptors has a unique anatomical distribution in the central nervous system, the peripheral nervous system and the gastrointestinal tract. Most of the clinically used opioids exert their desired therapeutic action (i.e. analgesia) at the mu receptor subtype.
Opioids include morphine, codeine, oxycodone, hydrocodone, hydromorphone, and the like. Examples of marketed opioids in the United States include OxyContin®, Vicodin®, and Percocet®. The opioids have diverse effects, including analgesia, euphoria, drowsiness, changes in mood and alterations of the endocrine and autonomic nervous systems. Opioid analgesics comprise the major class of drugs used in the management of moderate to severe pain. As a class, opioids are among the most prescribed drugs in the US. IMS data shows that about 9 billion hydrocodone containing pills are prescribed annually.
One of the major concerns with the prescription of opioids is the diversion of the drugs for non-prescribed use. It has been found that unused prescription opioid drugs are frequently diverted to people who misuse or abuse them without prescriptions. More than three out of four people who misuse prescription painkillers use drugs previously prescribed to someone else. For example, among new abusers who began to misuse pain relievers in the past year, 68 percent obtained their pills from a friend or relative, while only 9 percent purchased their pills from a friend, dealer, or over the internet. Strategies aimed at reducing the diversion of the vast surplus of unused prescription opioids are currently limited to programs aimed at encouraging people to “responsibly and appropriately” dispose of their leftover prescriptions. However, only a small percentage of unused opioid prescriptions are disposed of responsibly and appropriately because patients often reserve surplus pills for self-medication or recreational abuse. A critical aspect enabling the widespread issue of opioid diversion relates to the fact that the potency of prescription opioids diminishes very little over time. The long half-life of unused prescription opioids enables them to be stored, diverted, and abused almost indefinitely.